Hydrogenation of organic nitriles to primary amines, as aminomethyl groups, can be accomplished via the use of a Raney sponge nickel or cobalt aqueous slurry catalyst or precious metal catalysts. The nitrile and catalyst are charged into a stirred autoclave, oxygen is removed by reducing pressure or applying heat or both or by sparging with hydrogen or an inert gas, the autoclave is pressurized with hydrogen and heated to temperature. After completion of the reaction the primary amine is separated from the slurry catalyst by decantation or filtration. Fixed bed reactors have been used in an analogous way. Unfortunately, this process, without more, often produces undesirable quantities of secondary and tertiary amines, also known as "heavies." Attempts to reduce the amount of secondary and tertiary amines have generally involved the use of additives to the initial charge. For instance, when 25% nitrile in an ether solvent is hydrogenated in the presence of 5 to 15% water, catalyst and ammonia has been found to yield about 93% primary amine. Consider also, that when an aliphatic dinitrile is hydrogenated in the presence of water, 1 to about 100 wt. % ammonia based on nitrile and catalyst, that the heavies can be as low as 2.3% at maximal ammonia usage. In a different lab, a rhodium catalyst was used in conjunction with water, an alkali metal hydroxide and an immiscible organic solvent such as alkanes, aromatic or alicyclic hydrocarbons to hydrogenate an organic nitrile group. If hydrogen cyanide is not objected to, the cautious investigator may find it of interest that the hydrogenation of acetonitrile to ethylamine in basic aqueous solution may be carried out in its presence. Additionally, Raney cobalt, in combination with 0.5 to 4% water may be used to produce C4 to C12 amines.
Perhaps the prototypical prior art process for the hydrogenation of fatty acid nitrites is as follows: fatty acid nitrile is mixed with 1-2 wt. % water, 0.1 wt. % alkali metal hydroxide, Raney nickel catalyst, sparged with hydrogen to remove dissolved oxygen, and hydrogenated at 200 psi at 140.degree. C. for 110 minutes to yield fatty amine at 78% yield.
In a prior art industrial (ca. 5 mt capacity) autoclave process to produce a primary amine, dimer diamine from an organic nitrile, dimer dinitrile, an autoclave was fed an approx. 4200 kg charge that ultimately comprised dimer dinitrile, about 0.8 wt. % water, about 0.1 wt. % sodium hydroxide (about 16% of catalyst) and about 2 to about 2.4 wt. % Raney nickel. The process comprised the following steps:
1) Charging the organic nitrile to an autoclave. PA1 2) Removing oxygen from the organic nitrile, in this reactor, by heating the dimer nitrile under vacuum and breaking vacuum with an inert gas such as nitrogen. PA1 3) Adding Raney catalyst slurry and aqueous alkali metal hydroxide, about 0.2 wt. % of about 50 wt% sodium hydroxide, under the inert gas blanket. PA1 4) Drying the charge to less than about 0.1 wt. % moisture, in this reactor by pulling a vacuum of at least about 686 mmHg and heating to about 127.degree. C. PA1 5) Cooling the autoclave to below the boiling point of water, about 88.degree. C. PA1 6) Adding water, about 0.77 wt. %, to the charge. PA1 7) Pressurizing with hydrogen, to about 200 to about 400 psi. PA1 8) Heating the converter, to about 160.degree. C. PA1 9) Controlling the reaction exotherm that occurs by, for instance, restricting hydrogen feed and using cooling water. PA1 10) Cooling the resulting amine when the reaction is complete PA1 11) Separating the primary amine from the catalyst, by filtering or decanting, to obtain the desired primary amine product, which may then be optionally distilled.
Total amines yield is greater than 95%. The product specifications are a primary amine value of 185 minimum and a secondary plus tertiary amine value of 15 maximum. The dimer amine typically obtained contains 3-4% moisture and 5% secondary and tertiary amines, for a process yield of about 91% primary amine. The product typically has an amine value of about 191 and a secondary plus tertiary amine value of about 2.5 to 3.5% and a Gardner color of about 9.7.
Note here that water is being added to the initial charge from the sodium hydroxide solution and from the catalyst, as Raney nickel catalyst is shipped as a nickel sponge powder slurry in 50% water to avoid pyrophoric ignition. The water is present as a supernatant fluid which is decanted prior to adding catalyst to the charge. Variability in the settling and compaction of the catalyst leads to some uncertainty as to exactly how much water is being added to the charge, perhaps explaining the current industry practice to dry the charge, to get a consistent baseline, and then to add back a specific amount of water, so as to get repeatability in the process and product. While the percent variability in the water charge may not be high when the water content in the catalyst is low compared to the total added water desired, a high amount of water in the charge is not desirable when low-moisture content product is desired, such as when the product is intended for use in making polyurethanes.